1. Field of the Invention.
This invention relates to the field of clinical thermometers. In particular, this invention relates to clinical thermometers having a probe with a thermopile mounted thereon. More particularly, this invention relates to a clinical thermometer in which the temperature of the cold or reference junctions of a thermopile is measured by a resistance thermometer. Further, this invention pertains to a clinical thermometer wherein a resistance thermometer is included in an electrical bridge circuit which is used to compensate for temperature fluctuations at the cold or reference junctions.. The bridge circuit is connected to a meter which visually indicates the temperature sensed by the hot junctions of the thermopile.
2. Prior Art.
Clinical thermometers employing a thermocouple sensor are well known in the art. For example, Rentz U.S. Pat. No. 3,464,864, Jones U.S. Pat. No. 3,507,153, Moore U.S. Pat. No. 3,531,992 and Jarzembski U.S. Pat. No. 3,688,580 show devices utilizing a thermocouple for measuring the body temperature of animals and humans. In devices such as that shown in the Rentz patent, a thermocouple is used to measure the skin temperature of animals. The thermocouple is part of a button securing mechanism which holds the thermocouple to the skin surface of the subject. In devices such as described in the Jones and Moore patents, a thermocouple is inserted into the ear canal covered with a cotton membrane which leads to temperature inaccuracies due to the cotton membrane insulating properties. The Jarzembski patent discloses a disposable thermocouple probe and a connecting device which provides mechanical and electrical connection between the probe and a measuring and indicating assembly. The reference junction in the Jarzembski patent is provided within a thermally regulated oven which is maintained at a predetermined temperature and so no temperature compensation means are employed.
Temperature measuring devices employing a thermopile sensor are also known in the art. For example, Evins U.S. Pat. Nos. 1,552,284, 1,610,271 and 1,648,939 disclose thermopile sensors for measuring the external skin or body temperature. Other thermopile sensors and various methods for forming the sensors are shown in Thorpe U.S. Pat. No. 1,706,419 and Canada U.S. Pat. No. 2,562,696.
The use of a thermally sensitive resistor connected to compensate for changes in the temperature of the reference junction of a thermocouple and thermopile sensor are shown in Engelhard U.S. Pat. No. 3,225,597 and Wescott U.S. Pat. No. 3,580,074, respectively. However, these devices do not provide a disposable probe or a connector housing having a resistance thermometer for detachably mounting the probe.
In devices such as those shown in Glick U.S. Pat. No. 3,485,102 and in Ensign U.S. Pat. Nos. 3,367,186 and 3,500,280, thermistors are embedded in the end of a probe member attached to a meter having a dial reading in degrees of temperature for measuring a particular cavity temperature. These patents show the probe member being detachable from the rest of the temperature sensing system; however, these devices rely on thermistors which are quite different from thermopile sensors.
Other devices such as that shown in Moses U.S. Pat. No. 3,153,769, Catlin U.S. Pat. No. 3,402,378 and Biber U.S. Pat No. 3,221,555 use thermistor-type sensing mechanisms wherein the temperature sensor is encased and temperature discrepancies may occur due to conduction losses. Additionally, in such devices the probe is not electrically or mechanically attachable to a connector housing which contains a resistance thermometer.